Error

​Types of Errors

• Syntax

• Linker

• Run-time

• Logical

Syntax Errors

• Violation of C++ syntax rules

• Compile-time errors

• Most common:

  • Missing a symbol, e.g. one of: , . ( ) { } [ ] ; + - * /

    • Most common: ; and }

  • Use before declaration

  • Putting a symbol where it doesn’t belong

  • 5 = x;

Linker Errors

• Occur after compilation (during linking)

• Executable file cannot be produced

• Most common:

  • Missing header file

  • Incorrect header file

  • Incorrectly named function, e.g. Main instead of main

Runtime Errors

• Occur during program execution

• Not caught by compiler (usually no line number information)

• Most common:

  • Divide by 0

  • Attempt to access inaccessible memory

    • Null pointer dereference

    • Segmentation Fault

  • Out of memory

Logical Errors

• Occur during execution

• Program runs, but gives incorrect result

• Most common:

  • Off by one

  • Using = instead of == in a conditional

  • Infinite loops

  • Integer division

  • Array access out of bounds

  • Uninitialized variables

What to do when there's an error

• If there is an error message, READ IT

  • Compile-time errors will tell you what the error was, which file contains the error and the number of the line at which the error was discovered.

  • Linker errors will tell you what thing couldn’t be found, from which you can often figure out why it couldn’t be found.

  • Runtime errors will tell you what went wrong, from which you can narrow down to where in the code the kind of thing that went wrong could have gone wrong.

  • If you don’t understand the error message, ask for help understanding the error

• Start debugging

  • cout is your friend.

Writing code with fewer errors

• Start small

• Test often

• Work on one thing at a time

• Start debugging

  • cout is your friend.